The present invention relates to a strip diode laser having a glass fiber coupled to its output for transmission of its output signal. More particularly, the present invention relates to an arrangement for coupling the output of strip diode laser to an optical transmission fiber in a manner whereby the coupling is in a reactance free manner.
In glass fiber systems for the optical transmission of data employing semiconductor lasers as the transmitter, reflections at fiber connections and other irregularities in the course of the fiber adversely influence the desired operation of the laser transmitter. Such reflections change the natural frequencies and the life of the photons in the laser resonator and thus also the frequency and amplitude of the individual laser oscillations. Since the glass fibers employed in optical data transmission systems are extremely low in attenuation, reflections occurring at the laser output from remote fiber interference also have a noticeable effect. At the laser output such far away reflections quickly change in phase with the frequency, and experience considerable changes in phase when there are slight time changes in the fiber transmission properties.
As a result of these considerable, and under certain circumstances rapid, changes in phase of the reflections, the oscillation conditions for laser oscillations change approximately to the same degree. This results in fluctuations of the oscillation amplitudes. In the receiver, these fluctuations in amplitude are superposed on the signals with which the laser oscillations were modulated. The modulation characteristics of the laser injection controlled by the signals may experience extensive distortion as a result of the rapidly rotating reflections. As a whole, this noticeably interferes with, or even makes completely impossible, the normal operation of the laser transmitter.
To suppress such interference, the effect of these hardly avoidable reflections on the laser must be eliminated.